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Current network access control (NAC) technologies are not persistent enough, a security vendor has warned.

Dominic Wilde, product management veep at Nevis Networks, said that most NAC schemes rely on out-of-band appliances which check whether a client device is "clean", and once it passes muster they grant it access.

This makes them easier to install and remove, but he said it also means that once a client has been approved, there's no further control over where the user can go on the network or what they can do there.

"The first thing you need in the security world is to be stateful, so you understand the request going out and marry it to the response coming back," he said.

The second, he added, is to persistently track the user's identity: "Networks are by nature anonymous - you have MAC and IP addresses, but that's meaningless when customers are trying to solve compliance issues of who has access to what and when."

Needless to say, Nevis's security gear doesn't suffer this flaw, Wilde claimed. It sells an in-line security appliance and a secure access switch, both of which have built-in logic capable of controlling what the user can do and where they can go on the network. It also doesn't need agent software on the client to ensure it stays clean, he said.

Speaking as Nevis opened its UK office this week and began recruiting resellers for its devices, Wilde added that part of the problem is that most NAC technology operates at Layer 2 - the switching layer - using techniques such as virtual LANs to quarantine infected PCs.

"People are taking technologies designed for networking and applying them to security, and that's not what they're designed for," he said. Instead, they should work at Layers 3 and 4 - the routing and TCP layers - drawing user information from the corporate directory and using it to create an access policy for each user, he added.®